Currently, several countries are served by more than one international telephone common carrier--each referred to hereinafter as a carrier--and the number of countries so served is expected to grow in the future. Each carrier that supplies telephone traffic to a foreign country having multiple carriers desires that the carriers in that foreign country return to it a "fair" amount of telephone traffic. Such fair amounts are typically contracted for by representatives of the carriers and, most often, are related to the percentage of total intercountry telephone traffic each carrier supplies to the other.
Prior art systems for insuring the return of fair amounts of telephone traffic require the use of special trunking, routing and screening arrangements. One such prior art system forces telephone traffic to be delivered to a switch from which telephone traffic exits a carrier's network to enter the network of another carrier. Such a switch is called an egress switch. It is solely the responsibility of the egress switches to route telephone traffic to each carrier in a foreign country, as prescribed by the fair amounts agreed upon. However, this prior art system can not guarantee the return of the prescribed fair amounts of telephone traffic. As such, each carrier must account to its contracting partners for any discrepancies that result between the contracted for fair amounts and the actual traffic delivered.
The introduction of the ability to perform multiple homing routing, such as Split Access Flexible Egress Routing (SAFER), which is well known to those skilled in the art, has not corrected this problem. This is because telephone calls are still only assigned to a particular carrier at an egress switch. Moreover, each call loses the identity of its assigned carrier should it be necessary to return, or "crank", the call back to the switch at which the call originated (originating switch) for alternative routing instructions. (An egress switch cranks calls destined for foreign countries back to the originating switch in the event the egress switch cannot complete the call because, for example, no trunks to the assigned carrier are available.) As a result, when the originating switch routes a call that was cranked back to another egress switch, there is no guarantee that the new egress switch will assign the call to the same carrier to which the original egress switch had assigned the call. Therefore, it is not possible to accurately control the amount of telephone traffic delivered to each carrier, and hence, to return to each carrier its contracted for fair amount.
This inability to guarantee the return of prescribed fair amounts of telephone traffic also exists in prior art systems of the type using dedicated trunks to pass a call from an egress switch unable to complete a call to the carrier it chose to another egress switch serving the same carrier. This is because the call can only be forwarded to one additional egress switch and it is not guaranteed that this additional egress switch can complete the call to the originally selected carrier. If the call is not completed by the additional egress switch, the call is lost.
Another prior art system, carrier specific routing, which is not employed for purposes of returning a fair amount of traffic, assigns a carrier to a call at an adjunct processor associated with the originating switch based on the telephone number of the party paying for the call. The originating switch sends an indication of the assigned carrier with the call information if it routes the call to an egress switch. However, in such a case, no indication of the assigned carrier is retained in the originating switch. As a result, once a call is assigned a carrier in carrier specific routing, there is no possibility of changing the assignment. Furthermore, if the call is not completed to the assigned carrier by the egress switch or a single additional egress switch connected to the egress switch by dedicated trunks, as described above, the call is lost.